Selectively damped travelling wave tube

ABSTRACT

A travelling wave tube, with a delay line in the form of a wave guide having a plurality of slot-coupled disks secured thereto, has an elongate dielectric member received in aligned apertures of said disks. The dielectric member carries a plurality of metallized patterns which function to selectively damp electromagnetic waves of relatively high frequency, to suppress unwanted modes within said tube.

Unite States Patent [1 1 Gross 1541 S1CL1( "1'1V1LY [)AMlldl) 'lRAVlCLLlNG WAVE TUBE I [75] Inventor: Franz Gross, Munich, Germany [73] Assignee: Siemens Aktiengesellschaft, Berlin & Munich, Germany [22] Filed: June 15, 1973 [21] Appl. No.: 370,376

[30] Foreign Application Priority Data June 28, 1972 Germany 2231695 [52] [1.8. C1 315/35, 315/36, 330/43 [51] Int. Cl. HOlj 25/34 [58] Field 01 Search 315/35, 3.6; 330/43 [56] References Cited UNITED STATES PATENTS 3,324,338 6/1967 Winslow 315/35 3,329,855 7/1967 Landsbergen.... 315/3.5 3,345,533 10/1967 Washburn, Jr 315/36 [451 Aug. 27, 1974 3,365,607 1/1968 Rue-U. ct n1 315/35 3,397,339 8/1968 Beaver et a1 315/35 3,412,279 11/1968 Allen et a1. 315/35 3,453,491 7/1969 Cerko 315/35 3,466,494 9/1969 Eichin et a1 315/35 3,543,195 11/1970 King 315/35 X Primary ExaminerArchie R. Borchelt Assistant Examiner-Saxfield Chatmon, Jr.

Attorney, Agent, or Firm-Hi1], Gross, Simpson, Van Santen, Steadman, Chiara & Simpson 57] ABSTRACT A travelling wave tube, with a delay line in the form of a wave guide having a plurality of slotcoupled disks secured thereto, has an elongate dielectric member received in aligned apertures of said disks. The dielectric member carries a plurality of metallized patterns which function to selectively damp electromagnetic waves of relatively high frequency, to suppress unwanted modes within said tube.

13 Claims, 4 Drawing Figures PATENTEDMJBZTW M32593 SHEH 20? 2 SELECTIVELY DAMPED TRAVELLING WAVE TUBE BACKGROUND 1. Field of the Invention The present invention relates to travelling wave tubes and, more particularly, to travelling wave tubes with means for selectively suppressing undesired wave energy of relatively high frequency.

2. The Prior Art It is known to employ a delay line in connection with a travelling wave tube for filtering the wave energy made available at the output of the tube. Efficiency of operation is impaired by relatively high frequency energy which can be generated during the operation of the delay line and which is higher than the operating frequency of the apparatus.

The unwanted energy is easily suppressed by inserting a layer of damping material into the interior of the delay line. However, this remedy suppresses desired energy as well as the undesired energy, thereby serving to reduce the efficiency of the tube and reduce the amount of power available at the output.

A different arrangement has been suggested for use with special types of delay lines, such as those having a clover leaf structure. Such a system is disclosed in the German Offenlegungsschrift 1,566,031. As disclosed therein, a delay line is selectively damped by providing a wave guide, coated with damping material, coupled to the delay line, with the lower cut-off frequency of the wave guide located above the operating frequency band, by means of suitable longitudinal dimensioning of the wave guide. Such a wave guide must be embedded into the delay line in such a way that it extends across the E-field area of the unwanted wave energy. Such a damping arrangement is not only limited to special types of delay lines, but also is relatively complicated and costly.

It has also been suggested, in connection with delay lines having generally spiral-like structures, to provide a dielectric member having a layer of damping material adjacent to the delay line and associated with resonant circuits coupled to the delay line for elimination of the unwanted waves. In such a tube, the resonant circuits absorb and damp essentially only wave energy having frequencies within a relatively narrow band. Accordingly, the unwanted modes are heavily damped, but the operating frequency band is damped relatively little. The electrical behavior of the tube in the operating frequency band is generally unaffected by the additional structure. No equally satisfactory arrangement has yet been proposed, however, for travelling wave tubes having delay lines constructed in the form of a wave guide having a plurality of slot-coupled disks, such as that described in U.S. Pat. No. 3,015,750, for example.

SUMMARY OF THE INVENTION It is a principal object of the present invention to pro vide a system for providing selective damping of unwanted wave energy within a travelling wave tube having a delay tube in the form of a wave guide with slotcoupled disks.

Another object of the present invention is to provide a mechanism for accomplishing this result efficiently, with relatively little complication and expense.

In one embodiment of the present invention, there is provided a travelling wave tube with a delay line of the type having a plurality of slotted disks, and a dielectric member coupled with the wave guide and having, on its surface, a metallized pattern forming a damping line structure for selectively damping high frequency wave energy.

BRIEF DESCRIPTION OF THE DRAWINGS Reference will now be made to the accompanying drawings in which:

FIG. 1 is a longitudinal cross-sectional view of an illustrative embodiment of the present invention;

FIG. 2 is an enlarged view of a portion of the apparatus of FIG. 1;

FIG. 3 is a longitudinal cross-sectional view of an alternative embodiment of the present invention; and

FIG. 4 is a longitudinal cross-sectional view of another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, the output circuit of a travelling wave tube incorporating an illustrative embodiment of the present invention is shown. A high power amplifier tube (not shown) is adapted to produce a relatively high current in the form of an electron beam, which passes through the central axis of a delay line 1. The delay line consists of a plurality of copper disks 2, which are welded together at their edges with intermediate rings 3, to form a unitary structure. The copper disks 2-are each provided with a tubular central portion 4, and the electron beam passes through the tubes 4, which are axially aligned. The electron beam enters the delay line from the left-hand side (as viewed in FIG. 1) and passes through all the tubes 4, leaving the delay line at the right-hand side. The apparatus for generating and receiving the electron beam is not illustrated, as it is preferably of conventional construction. A plurality of aligned apertures 5 and 6 are provided, with the apertures 5 of alternate disks being aligned on one side of the beam, and the apertures 5 of the remaining disks being aligned on the opposite side of the beam. The apertures 6 are provided only on the remaining disks.

An output wave is produced by means of a decoupling chamber 7, which is interconnected with the space between the two endmost disks 2; and it is connected with a tapered bridge wave guide 8, adapted for receiving the energy and communicating it to a utilization device (not shown).

A dielectric rod 9 is positioned at a location generally parallel to the axis of the tubes 4 and is received in the aligned apertures 5 and 6 of all of the disks 2.

The apertures 5 are larger than the apertures 6, and serve to couple adjacent chambers interposed between adjacent ones of the disks 2. The apertures 6 are just large enough to receive the rod 9. The rod 9 is mounted in a fixed manner by means of a socket 11 secured to an end of the delay line, and the other end of the rod 9 is supported by means of a bearing 12 on the opposite end wall of the delay line. The bearing 12 is adapted to permit free longitudinal motion of the rod 9, in order to accommodate expansion and contraction of the rod 9 during heating and cooling thereof. The left-hand end of the rod 9 is provided with a coating 13 of damping material, which is preferably a thin layer of graphite.

This area is adapted to absorb energy at the operating frequency which is partially reflected from the axis of the tube.

The other right-hand end of the rod 9 is provided with means for the selective suppression of unwanted wave energy, which represents unwanted modes. The rod 9 is preferably formed of beryllium oxide, and passes through the apertures 5 and 6 without making contact with them.

A plurality of conductive structures are coated onto the surface of the rod 9, each structure 15 being located in the vicinity of an aperture 5. The structures 15 are shown in enlarged scale in FIG. 2. They take the form of a series of lines of conductive material, such as metal printed or otherwise placed on the surface of the rod 9. The lines are connected to form a comb-like arrangement 16, with a plurality of teeth 17 interconnected at one end by a longitudinal strip of conductive material. The opposite ends of the teeth 17 contact a strip of damping material 19, which preferably is formed of the same material as the layer 13. The metallized structure 15 and the damping layer 19 are formed by placing relatively thin layers of the appropriate material on the surface of the rod 9, by means of conventional techniques.

The length of the teeth 17 is approximately equal to about a quarter wave length of the unwanted wave energy, and such waves are selectively damped in a very efficient manner. As shown in FIG. 1, the teeth may be graduated in length to damp waves of different frequencies. There is thus formed a chain of resonators made up of the structures 15 which are coupled with the delay line 1 only in the frequency band of the unwanted wave energy, because the resonators are adapted to resonate only at the wave lengths of the unwanted energy. The resonator chain accordingly loads the delay line in such a way that the unwanted modes are practically completely eliminated during operation of the travelling wave tube.

The structures 15 are adjusted in a way which provides for the most effective damping of the unwanted waves; and, for this purpose, the structures are located in the vicinity of the apertures 5, and the teeth 17 are oriented in such a way that the orientation of the E- field of the desired operating mode is normal to the surface of the damping strip. In one embodiment of the present invention, the damping of the operating mode is increased by the structures 15 by a factor of approximately 2, while the damping of the unwanted modes is increased by the factor of 20 to 50.

Although the desired operating mode in the working area of the delay line is damped relatively little, the damping is considerably heavier near the 2 1r point of the delay line. This feature is advantageous in providing protection against the exciting of the so-called 2 1r point oscillation, which is especially critical with the slotted disk construction of the delay line illustrated.

In an alternative embodiment of the present invention, the inner surfaces of the tubes 4 may be lined with a metallic coating of a metal having a relatively high melting point, to prevent vaporization of the copper of which the disks 2 are formed. One material which may be used for this purpose is rhodium. Such a coating protects the rod 9 from receiving a deposit of copper as a result of vaporization of copper from the interior of the tubes 4 during periods of poor electron beam focusing. When a rhodium layer is employed, the rod 9 is protected from such a copper deposit without any increase in the high frequency losses and without any reduction in the heat conduction capability of the rod 9.

An alternative embodiment of the present invention is illustrated in FIG. 3. The arrangement of FIG. 3 resembles that shown in FIG. 1, except that a pair of rods 9 and 10 are employed instead of the single rod 9 used in the apparatus of FIG. 1. The rods 9 and 10 are each received in aligned apertures of the copper disks 2 on opposite sides of the axis of the tubes 4, each disk 2 having one aperture 5 for receiving one of the rods 9 and 10 and another aperture 6 for receiving the other rod. As explained above, the apertures 5 are larger than the apertures 6, to facilitate coupling between the spaces enclosed between adjacent pairs of the disks 2.

The mounting arrangement for the rods 9 and 10 is also somewhat different in the embodiment illustrated in FIG. 3. The rods 9 and 10 are received in the end wall 26 of the delay line by means of cooperating screw threads on the rods and on the interior surface of a bore provided in the wall 26 for each of the rods. A pair of heat conductive tubes 22 and 23 are connected with the ends of the rods 9 and 10, and serve to rapidly conduct heat away from the rods 9 and 10 to a suitable heat sink. Elongation due to expansion with heat is provided automatically by the rods 9 and 10 shifting axially relative to the apertures 5 and 6.

Another embodiment of the present invention is illustrated in FIG. 4. This embodiment is similar to that illustrated in FIG. 3, except that an alternative mounting arrangement for the rods 9 and 10 is illustrated. The rod 9 is soldered to an intermediate copper disk 24, and the rod 10 is soldered to a different copper disk 25. The disks 24 and 25 are both arranged near the central portion of the delay line, so that the movement of the ends of the rods 9 and 10, in response to heating, is reduced. The soldering increases the mechanical stability of the assembly as well, and provides for a good heat conduction from the rods 9 and 10 to the body of the delay line, through the disks 24 and 25.

It will be apparent to those skilled in the art that the apparatus of the present invention may be modified in certain respects, both in the construction of the delay line and in the arrangement of the damping patterns 15. Alternative damping structures may take the form of coils or inter-digital lines with overlapping teeth, all formed of conductive material, with damping material, such as graphite, applied to the surfaces of the rods. In addition, dielectric rods, such as the rods 9 and 10, may be directed outside of the axis of symmetry of the delay line, to damp unwanted operating modes with asymmetrical field distribution.

What is claimed is:

1. For use with a travelling wave tube, a delay line comprising a wave guide having a plurality of spacedapart, slot-coupled disks, an elongate dielectric rod extending parallel to the axis of said delay line, said rod having a surface layer of damping material and a metallized structure formed as a layer on the surface of said rod, said metallized structure being coupled with said delay line for attenuating wave energy of a selected frequency, said rod being received in aligned apertures provided in said disks, and including means for rigidly supporting said rod at one end, whereby said rod is suspended within said apertures out of contact therewith.

2. Apparatus according to claim 1, wherein said structure is positioned on said rod in the vicinity of alternate ones of said apertures.

3. Apparatus according to claim 1, including a plurality of spaced-apart metallized structures, each of said structures being positioned on said rod in the vicinity of alternate ones of said apertures.

4. Apparatus according to claim 1, wherein said metallized structures comprise a plurality of tooth-like strips, said tooth-like strips being equal in length to approximately one-quarter wavelength of the wave energy which is to be selectively suppressed.

5. Apparatus according to claim 4, including a strip of damping material applied to the surface of said rod, said damping strip joining a common end of each of said tooth-like strips.

6. Apparatus according to claim 5, including a strip of conductive material joining the ends of said tooth like strips which are opposite said common ends.

7. Apparatus according to claim 4, wherein said tooth-like strips are oriented in a plane normal to the direction of the E-field lines of the desired wave energy of the operating mode of the tube.

8. Apparatus according to claim 1, including a further layer of damping material applied to the surface of said rod, for damping wave energy of the operating mode of the tube.

9. Apparatus according to claim 1, wherein said disks are provided with a surface coating of a metal having a high melting point in the vicinity of the electron beam with said delay line. 1

10. Apparatus according to claim 1, including two dielectric rods, said rods being received in aligned apertures provided in said disks on opposite sides of the axis of said delay line, and a plurality of said conductive structures mounted on the surfaces of said rods, said structures being spaced in rows along the length of said rods, with the structures of one rod arranged to be equally spaced between the structures of the other rod.

11. Apparatus according to claim 1, including a soldered connection between said rod and one of said disks.

12. Apparatus according to claim 1, including means for independently supporting both ends of said rod, one of said supporting means being adapted to allow free axial movement of said rod.

13. For use with a travelling wave tube having a delay line formed of a plurality of slot-coupled disks spaced along the axis of the delay line, the method of selectively damping unwanted wave energy within said delay line, comprising the steps of; placing a dielectric rod parallel to the axis of said delay line within aligned apertures provided in said disks, and placing a metallized structure on the surface of said rod to form a resonant circuit adapted to resonate at the frequency of said unwanted wave energy. 

1. For use with a travelling wave tube, a delay line comprising a wave guide having a plurality of spaced-apart, slot-coupled disks, an elongate dielectric rod extending parallel to the axis of said delay line, said rod having a surface layer of damping material and a metallized structure formed as a layer on the surface of said rod, said metallized structure being coupled with said delay line for attenuating wave energy of a selected frequency, said rod being received in aligned apertures provided in said disks, and including means for rigidly supporting said rod at one end, whereby said rod is suspended within said apertures out of contact therewith.
 2. Apparatus according to claim 1, wherein said structure is positioned on said rod in the vicinity of alternate ones of said apertures.
 3. Apparatus according to claim 1, including a plurality of spaced-apart metallized structures, each of said structures being positioned on said rod in the vicinity of alternate ones of said apertures.
 4. Apparatus according to claim 1, wherein said metallized structures comprise a plurality of tooth-like strips, said tooth-like strips being equal in length to approximately one-quarter wavelength of the wave energy which is to be selectively suppressed.
 5. Apparatus according to claim 4, including a strip of damping material applied to the surface of said rod, said damping strip joining a common end of each of said tooth-like strips.
 6. Apparatus according to claim 5, including a strip of conductive material joining the ends of said tooth-like strips which are opposite said common ends.
 7. Apparatus according to claim 4, wherein said tooth-like strips are oriented in a plane normal to the direction of the E-field lines of the desired wave energy of the operating mode of the tube.
 8. Apparatus according to claim 1, including a further layer of damping material applied to the surface of said rod, for damping wave energy of the operating mode of the tube.
 9. Apparatus according to claim 1, wherein said disks are provided wiTh a surface coating of a metal having a high melting point in the vicinity of the electron beam with said delay line.
 10. Apparatus according to claim 1, including two dielectric rods, said rods being received in aligned apertures provided in said disks on opposite sides of the axis of said delay line, and a plurality of said conductive structures mounted on the surfaces of said rods, said structures being spaced in rows along the length of said rods, with the structures of one rod arranged to be equally spaced between the structures of the other rod.
 11. Apparatus according to claim 1, including a soldered connection between said rod and one of said disks.
 12. Apparatus according to claim 1, including means for independently supporting both ends of said rod, one of said supporting means being adapted to allow free axial movement of said rod.
 13. For use with a travelling wave tube having a delay line formed of a plurality of slot-coupled disks spaced along the axis of the delay line, the method of selectively damping unwanted wave energy within said delay line, comprising the steps of; placing a dielectric rod parallel to the axis of said delay line within aligned apertures provided in said disks, and placing a metallized structure on the surface of said rod to form a resonant circuit adapted to resonate at the frequency of said unwanted wave energy. 